D150 wiring issues, help!

my fuel gauge and temp gauge only reading about 1/8 of what thay should! issue comes and gose, gauge respond fine 95% of the time! i dont like it and feel issue needs resolved before it becomes a bigger issue! ol truck ant been messed with much, only couple places wiring been opened from factory wraping! also every now and then motor run like it ant getting good voltage to ignition, but same as gauges just dose it enuff to want fix it! any body have similer issues??? any idea where or what to look at?? bulk head connectors are clean and in good shape!
You didn't state what year you're working with, but, for most years, I'd start by getting a new IVR.....an electronic one. They're relatively cheap and can cure a whole host of gauge problems.